REDOX REACTION-MECHANISM OF CYTOCHROME-C AT MODIFIED GOLD ELECTRODES

The roles of surface modifiers (4-pyridyl derivatives) in the electron-transfer reaction of cytochrome c at a gold electrode surface were investigated by using ac impedance and electroreflectance techniques. It was found that there are at least three types of modifiers. Cytochrome c was immobilized on the bis(4-pyridyl) disulfide modified gold electrode, and the electron-transfer reaction between the electrode and cytochrome c in the bulk takes place through these immobilized layers on the electrode. The binding of cytochrome c to the irons-l,2-bis(4-pyridyl)ethylene-modified surface was weak, and the modified surface was partially covered by cytochrome c. The electrode reaction takes place through the adsorbed layer of the modifier on the electrode surface. The electrode reaction of cytochrome c at the bare electrode surface also takes place in this case with a formal potential about 440 mV more negative than the potential of native cytochrome c. Cytochrome c was coadsorbed on the gold electrode with 4,4-bipyridine. The formal potential of cytochrome c coadsorbed with 4,4-bipyridine was about 225 mV more negative than the potential of the native one but more positive than that of cytochrome c adsorbed on the bare electrode surface. The reversible electrode reaction of cytochrome c in the bulk through the adsorbed layer of cytochrome c was very improbable in this case. The electrode reaction of the bulk species may take place through the adsorbed layer of 4,4-bipyridine. © 1990, American Chemical Society. All rights reserved.